Categorical perception is the ability to divide various wave lengths of light into separate groups of color. The concept of blue, red, purple, etc. are examples of this. For years, it was believed that humans were the only ones to possess the ability, however, it has been previously shown that birds are capable of categorizing colors as well.
As part of the mating process for Zebra finches, females will select the male with the reddest beak over those with light orange beaks (believed to be so due to red beaks being a sign of good health). Because of this natural predisposition toward certain colors, a research team decided to test whether the birds categorized other colors equally well.
The team tested the female Zebra finches by training them to seek out two-toned disks from single color disks by rewarding them with seeds. They found the birds to be quite capable of identifying two-toned red and orange markers and worked to establish threshold ranges for how similar various colors can be before the birds can no longer accurately tell them apart. Through testing, it was determined that the birds struggled with cool colors (green, blue, purple), compared to warm colors (red, orange, yellow) - a result shared with humans.
Read more: http://rsci.nl/efm
Image: JJ Harrison